Technical Abstract:
Degree of esterification (DE) is a primary determinate for applications involving pectin. It has been demonstrated that the yield stress behavior of pectin in the presence of calcium ions is dependent on the type of deesterification (ordered vs. random) as well as the overall DE, but these pectin structures were not characterized. This work will be important for new high-volume applications involving suspension such as using citrus peel for drilling muds or for paper additive products. More recently a non-calcium sensitive pectin with a 94 % degree of methylation was demethylated at lower degrees of methylation (DM) using a thermally tolerant pectin methylesterase to examine the affects on functional properties, such as rheology, relative to DM. Pectin’s functional properties and reactivity toward calcium and other cations is dependent on the amount of methylated galacturonic acid units and their distribution pattern within the homogalacturonan stretches formed from demethylation. Storage modulus (G') and calcium sensitivity increased with decreasing DM with maximum G' occurring at 50 % DM. Onset of storage modulus was observed at DM values near 70%. Storage modulus maximized when the pectin to calcium ratio reached a value of approximately 5 to 1. Recovery of storage and loss modulus after exposure shear, which is important for suspension, was determined as a function of pH at which the demethylation occurred and will be discussed. Mixing demethylated pectin with narrow-range size-classes of oligogalacturonic acids showed that small galacturonic acid oligomers with a degree of polymerization less than 25 has a significant affect on modulus and modulus recovery.